1. Field of the Invention
This invention relates to orthopedic surgery and, in particular, to devices and prosthesis for stabilizing and fixing bones and joints of the body.
2. Description of the Prior Art
Published U.S. Application, US 2003/0149487 A1, published Aug. 7, 2003, teaches the use of a linear movement to apply compressive forces to connect components of an artificial hip joint.
U.S. Pat. No. 6,626,906 issued Sep. 30, 2003 to Young teaches a spinal rod attached to a spinal anchor by a clamp. The clamp is tightened about the anchor by a collet screwed into the clamp. The rod is held in the clamp by a split ring that is reduced in size by the collet. The anchor is placed in the bone by torque and the collet is tightened by additional torque.
U.S. Pat. No. 6,610,063 issued Aug. 26, 2003 to Kumar et al, U.S. Pat. No. 6,610,062 issued Aug. 26, 2003 to Bailey et al, U.S. Pat. No. 6,565,565 issued May 20, 2003 to Yuan et al, U.S. Pat. No. RE 37,665 issued Apr. 16, 2002 to Ralph et al, U.S. Pat. No. 6,478,798 issued Nov. 12, 2002 to Howland and U.S. Pat. No. 5,584,834 issued Dec. 17, 1996 to Errico et al teach a spinal rod coupled to several bone anchors by clamps that require additional torque to be applied to the assembly after the bone screw has been seated in the bone.
In normal practice, the bone screws are each anchored in the bone with a specific amount of torque that approaches the ultimate sustainable force between the screw threads and the bone. The bone screws are then connected together by a rod having sufficient stiffness to maintain the desired skeletal orientation. The connection between the rod and the bone screws must be strong enough to be immobile.
All these prior art spinal fixation devices result in additional torque applied to the assembly, and thereby to the bone screw, to tighten and lock the rod to each of the bone screws. The additional load may strip the purchase between the bone and the threads of the bone screw. To prevent such a result, some tool must be used to counter the torque of locking the rod and the screws. The use of an anti-torqueing tool requires additional coordination by the surgeon or surgeons to prevent slippage.
What is needed in the art is a system for connecting a rod and an embedded bone screw using compressive forces rather than torque.